| Abstract | This work introduces methodological novelties in the field of trace metal speciation and organic matter in natural waters: (i) advancement of competitive ligand exchange - adsorptive cathodic stripping voltammetry; a new modes of multi detection window approach, (ii) revised application of copper (Cu) ion-selective electrodes in high chloride media i.e., seawater and (iii) a novel voltammetric method for quantification of humic substances. The second chapter of the thesis is dedicated to field studies in the Krka River estuary: (i) the dynamics and seasonality of dissolved organic matter (DOM) in the estuary and (ii) organic Cu speciation in the estuarine salinity gradient, (iii) the dynamics of various trace elements (Cu, Zn, Pb, Cd, Ni, Co, Cr, Fe, Mn, Al, As, V, U) and DOM in the estuarine surface microlayer (SML) and (iv) the size partitioning of different trace metals (Cu, Zn, Pb, Cd, Ni, Co, Fe, Mn and Al) in the salinity gradient. In winter, the estuarine waters contained a strong terrestrial signature, whereas in summer in situ production dominated the DOM pool. The high stratification combined with a decoupling between production and removal processes resulted in DOM accumulation above the halocline. In the bottom layer, DOM was released and quickly removed when oxygen was available, whereas in hypoxic waters the production of dissolved organic carbon and chromophoric DOM was linearly related to oxygen consumption. The Cu speciation study identified two ligand classes: L1 (12.5 < logK’CuL1 < 14.3) was mainly derived from recent phytoplankton production and L2 (10.6 < logK’CuL2 < 11.1) was characterised as predominantly humic substances of both terrestrial and autochthonous origin. Seasonal anthropogenic Cu input was successfully buffered by the ambient ligand pool due to the increased ligand concentrations in summer attributable to increased in situ production. The extensive SML samplings gave insights in diel variations of total and dissolved concentrations of trace elements in the SML, which were influenced by various factors: wind speed and wind direction, suspended particulate matter (primarily Fe, Al, Mn and Pb), complexation with organic ligands and bubble scavenging (primarily Fe, Cu and Pb) and bacterioneuston activity. The truly dissolved fraction (< 3 kDa) dominated the size speciation of Ni, Cd, Zn, Co and Cu, while Fe, Al, Pb and Mn were mainly present in particles larger than 5 μm. Of the studied metals, Pb, Al, Fe and Cu showed the highest affinity for colloids (3 kDa – 0.1 μm), which accounted for 30 – 37% of their dissolved pool (< 0.1 μm). |
| Abstract (croatian) | Ovaj rad uvodi nova postignuća vezana za metodologije specijacije metala u tragovima te karakterizaciju organske tvari, i to: (i) unapređenje metode kompetitivne izmjene liganada - adsorptivne voltametrije katodnog otapanja; novi pristup primjeni višestrukog raspona granica detekcije, (ii) revidirana primjena bakar (Cu) ion selektivnih elektroda u mediju s visokim udjelom klorida tj. morskoj vodi te (iii) nova voltametrijska metoda za kvantificiranje humičnih tvari. Drugi dio disertacije posvećen je terenskim istraživanjima u estuariju rijeke Krke: (i) dinamici i sezonalnosti otopljene organske tvari (OOT) i (ii) organske specijacije Cu u gradijentu saliniteta, (iii) dinamici različitih elemenata u tragovima (Cu, Zn, Pb, Cd, Ni, Co, Cr, Fe, Mn, Al, As, V, U) i OOT u površinskom mikrosloju estuarija (SML) te (iv) veličinskoj raspodjeli različitih metala u tragovima (Cu, Zn, Pb, Cd, Ni, Co, Fe, Mn, Al) u gradijentu saliniteta. Zimi su estuarijske vode karakterizirane autentičnom kopnenom OOT, dok ljeti dominira autohtona OOT. Izražena stratifikacija u kombinaciji sa smanjenom bakterijskom razgradnjom iznad halokline rezultirala je akumulacijom otopljenog organskog ugljika (DOC) u površinskom sloju estuarija. Nasuprot tome, u donjem morskom sloju, OOT se oslobađala i brzo uklanjala kada je kisik bio dostupan, dok je u hipoksičnim vodama proizvodnja DOC-a i kromoforne OOT bila linearno povezana s potrošnjom kisika. Studija specijacije Cu identificirala je dva razreda liganda: L1 (12.5 < logK’CuL1 < 14.3) nastalih primarno proizvodnjom fitoplanktona, te L2 (10.6 < logK’CuL2 < 11.1) okarakteriziranih kao pretežno humične tvari (kopnenog i autohtonog podrijetla). Sezonski antropogeni unos Cu uspješno je neutraliziran povećanom koncentracijom liganada ljeti koja se može pripisati povećanoj biološkoj aktivnosti u ovom periodu. Opsežna uzorkovanja SML-a dala su uvid u varijaciju ukupne i otopljene koncentracije elemenata u tragovima u SML-u pod utjecajem različitih čimbenika: brzina i smjer vjetra, suspendirane čestice (prvenstveno na Fe, Al, Mn i Pb), kompleksiranje s organskim ligandima i stvaranje potpovršinskih mjehurića (prvenstveno na Fe, Cu i Pb) te aktivnost bakterioneustona. Stvarno otopljena frakcija (< 3 kDa) je dominirala veličinskom raspodjelom Ni, Cd, Zn, Co i Cu, dok su Fe, Al, Pb i Mn bili prisutni primarno u česticama većim od 5 μm. Relativno mali postotak metala je bio prisutan u koloidima (3 kDa – 0.1 μm). Najveći afinitet prema koloidima pokazali su redom Pb, Al, Fe i Cu kod kojih su koloidi činili 30 – 37% otopljene frakcije (< 0.1 μm). |
